Using SharedPreferences with SQLiteOpenHelper before initialising the database

Question

I would like to have a database for each user of my app. Usernames are stored in SharedPreferences. So I'm looking for something like this:

public class DatabaseHelper extends SQLiteOpenHelper {

    final SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
    String LoggedInUser = sp.getString("user","");

    public static final String DATABASE_NAME = LoggedInUser + ".db";

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
    }

    public void onCreate(SQLiteDatabase db) {
        ...
    }
    ...

}

But this doesn't work, because SharedPreferences need context (using getApplicationContext() instead of this doesn't work either. This can be solved by something like this:

private Context appContext;
public DatabaseHelper(Context context) {
    super(context, DATABASE_NAME, null, 1);
    this.appContext = context;
}

And then accessing SharedPreferences afterwards.

But I need to access SharedPreferences before this method ("DATABASE_NAME" is used in the above method and I want to define "DATABASE_NAME" using SharedPreferences).

Is there any way for doing this?

Answer 1

Since call to super() must be first statement, the only solution to achieve it would be to pass the DATABASE_NAME as constructor parameter:

public DatabaseHelper(final Context context, final string dbName) {
        super(context, dbName, null, 1);
 }

You can then either implement factory or Facade pattern to construct or pass the value to DatabaseHelper or simply pass the dbName value from Activity/Fragment.

An example of Factory could be:

public final class DatabaseFactory {

    public static DatabaseHelper getDataBaseHelper(final Context context){
        final SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(context);
        final String loggedInUser = sp.getString("user","");
        return new DatabaseHelper(context,loggedInUser);
    }
}

In Activity you can access the Helper as follows:

public class MainActivity extends Activity{
    ...

    @Override
    public void onCreate(Bundle savedInstanceState) {
        ...
        final DatabaseHelper myDB = DatabaseFactory.getDataBaseHelper(this);
        ...
    }
}

Answer 2

Must you use SharedPreference in you SQLiteOpenHelper? I think you maybe use SQLite in your Activity, then how about declare SharedPreference in your Activity first, and get that in your SQLite through database's constructor.